// ==================================================

// C library
#include <cmath>
#include <climits>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>

// Containers
#include <vector>
#include <list>
#include <stack>
#include <queue>
#include <deque>
#include <set>
#include <map>

// Input/Output
#include <iostream>
#include <istream>
#include <ostream>
#include <sstream>
#include <fstream>
#include <ios>
#include <iomanip>

// Other
#include <string>
#include <bitset>
#include <algorithm>
#include <utility>
#include <iterator>
#include <limits>

// ==================================================

using namespace std;

typedef pair<int, int> PII;
typedef long long LL;

// ==================================================
#define oo ((1LL<<31) - 10);
#define max_(x, y) ((x) > (y) ? (x) : (y))
#define min_(x, y) ((x) > (y) ? (y) : (x))

#define PR(x) cout << #x " = " << (x) << "\t"
#define NL cout << "\n"

#define PRINT1(x) PR(x), NL
#define PRINT2(x1, x2) PR(x1), PRINT1(x2)
#define PRINT3(x1, x2, x3) PR(x1), PRINT2(x2, x3)
#define PRINT4(x1, x2, x3, x4) PR(x1), PRINT3(x2, x3, x4)

// ==================================================

template<typename T>
void PRINTC(const T& a) { cout << a << " "; }

template<typename T>
void PRINTA(const T ar[], int n) {
  for (int i = 0; i < n; ++i) PRINTC(ar[i]); NL;
}

template<typename T1, typename T2>
void PRINTP(const pair<T1, T2>& p) { PRINTC(p.first); PRINTLN(p.second); }

template<typename T>
void PRINTLN(const T& a) { cout << a << "\n"; }

template< typename T1, typename T2 >
void PRINTAV( T1 & vec, T2 x) {
  ostream_iterator< T2 > O( cout, " " );
  copy( begin( vec ), end( vec ), O ); NL;
}

// ==================================================


int main( void ) {

#ifdef DEBUG
  // freopen("1134.in", "r", stdin);
#endif

  ios::sync_with_stdio(false);
  cin.tie(NULL);

  string words[50]={"auto", "break", "case", "char", "const",
    "continue", "default", "do",
    "double", "else", "enum", "extern", "float", "for", "goto",
    "if", "int", "long", "register",
    "return", "short", "signed", "sizeof", "static", "struct",
    "switch", "typedef", "union",
    "unsigned", "void", "volatile", "while"};
  string s;
  cin>>s;
  for(int i=0;i<32;i++)if(words[i]==s)
                                        {
                                          cout<<"no\n";
                                          return 0;
                                        }
  if(s.size()>0&&isdigit(s[0]))
    {
      cout<<"no\n";
      return 0;
    }
  for(int i=0;i<int(s.size());i++)
    {
      if(s[i]=='_'||isalnum(s[i])) continue;
      else
        {
          cout<<"no\n";
          return 0;
        }
    }
  cout<<"yes\n";

  return 0;
}
